1. Field of the Invention
The present invention relates to a droplet ejection method and device, and more specifically relates to a droplet ejection method and device for ejecting droplets by the application of thermal energy.
2. Description of the Related Art
Microactuators are known which, by using thermal energy or the like to cause a liquid to fly onto a medium in the form of small particles (known as droplets), form images of patterns and the like or form bodily structures of the liquid. Inkjet printer head technology is widely known as a technology which utilizes one of the functions of these microactuators. That is, in a printer which utilizes inkjet technology, ink droplets are jetted to provide an image on a paper surface.
Microactuators eject some kind of functional liquid onto a medium, implement patterning, and thus provide functionality to the medium.
Microactuators that are known include, for example, microactuators which are used for fabricating color filters, microactuators which are used for fabricating microlenses, microactuators which are used in medical nanopipettes, microactuators which are used for fabricating sensors, microactuators which are used for producing plates, proof plates and the like, and the like.
As applications for microactuators in color filter fabrication technology, a technique relating to a method of arrangement when filter material is to be discharged (see Japanese Patent Application Laid-pen (JP-A) No. 2002-273869) and a technique of controlling thickness and volume when a color filter is to be fabricated (see JP-A No. 9-21909) have been proposed. Further, for cases of applying microactuators to the fabrication of microlenses, a technique of focusing ultrasonic waves on a liquid surface in order to dropletize a curable resin liquid (see JP-A No. 2003-90904), and a structure of a lens fabrication apparatus together with a technique for ejecting variable weight amounts of a lens material liquid (see JP-A No. 2003-53747) have been proposed.
Further still, the application of microactuators to inkjets which serve as pipettes, which are mainly for medical use, has been investigated (see JP-A numbers 2001-228162 and 2001-232245). For the application of microactuators to the fabrication of sensors, a technique of discharging organic material onto electrodes by inkjets to form thin-film sensors has been proposed (see JP-A No. 2000-97894 and the publication of JP-A No. 2000-97894). For the application of microactuators to the production of plates, proof plates and the like, a method of controlling a recording head when fabricating a planographic plate with an inkjet has been proposed (see JP-A No. 2002-205370). Further yet, as microactuators which utilize electric fields, technologies which utilize electric fields for methods of more stably applying functional liquids to media have been investigated (see JP-A Nos. 2001-301154 and 2000-246887).
Variability of discharge amounts, breadth of a range of such variability, larger ejection forces, and the ability to eject various kinds of functional liquid are sought after as characteristics of these microactuators. Piezo-type actuators which are dependent on electromechanical transduction operations, actuators which utilize electric fields, and thermal boiling-type (thermal inkjet (TU)) actuators which utilize rapid heating and boiling are available as actuators that realize these characteristics.
Thermal boiling-type microactuators, in which displacement amounts that are achievable per unit area are large, are preferable for achieving reductions in size, cost and the like of microactuators. For pulse systems which utilize usual inkjets, in which these thermal boiling-type microactuators are applicable, technologies in which a pre-heating bias is applied before rising of a discharge pulse, a signal is applied for preliminary heating without forming bubbles, and a volume of ejected droplets is altered by the pre-heating, and/or in which a heater-driving waveform is varied from a simple rectangular wave have been proposed (see JP-A Nos. 63-132059, 54-39470, 2-214664 and 2000-246899). However, with pulse signals which are heater-driving signals for ejecting ink that is used in inkjets, in a case in which a single heater-driving waveform is simply altered and used at a microactuator, as heretofore, an ejection force for jetting of a functional liquid is inadequate. In other words, conventional techniques provide stable ejection states, but do not consider ejection forces.
In order to achieve a large ejection force with a thermal boiling-type microactuator, it is necessary to control behaviors relating to the generation of bubbles, which is based on rapid heating and boiling due to the application of thermal energy. Therefore, it is necessary to consider such behaviors and provide thermal energy to provide such behaviors.